Visit London at the moment and they are easily spotted in that distinctive get-up.

The first sound people hear before they even arrive at a venue or Olympic Park is from the volunteers. The ones working what some call "the plum job", up above the crowd on high seats, lifting the mood.

They put shouts out to countries, Tube lines, for athletes that fans might worship. They check if anyone is "excited yet" today.

In a way it is so un-British. Ebullient, noisy, interactive - rather than reserved. But they are also dry and witty.

Volunteers' top overheard words

"Anyone here to cheer from the USA? Canada? East Timor? ...I've checked, it is an Olympic country."

"Big up for the Jubilee Line, for the overground trains - did you come in on the overground trains? Not for the Central Line - You've got delays."

"You have a great night now. Yes you, with the big smile there, no, not you, sir."

"Please take the queue on the left of the barriers for the Jubilee Line, the right for Central Line and overground trains. You look shocked madam. Don't worry, there's a hole in the barriers behind me - it's all a game..."

Games organisers Locog can't praise them enough. And there is a Twitter campaign to recognise their efforts under the hashtag #bigupthevolunteers. There are also London Ambassadors working across the city.

So how has it been for them, to give up a minimum of 10 days with no pay, no expenses, no accommodation, for some, sleeping in a bunk at a makeshift campsite?

"It has been absolutely amazing," says Margaret Singer, a speech and language therapist from Aberdeenshire.

She is a first-responder (first-aider) at the BMX track, built in the lee of the velodrome. She has worked at both venues treating minor ailments - mending trapped fingers, medicating headaches.

Does she mind having spent about £500 on fares to come south for training in the lead-up to and for the Olympics themselves?

"No, it's on the bucket list, one of the things you should do, go to the Olympic Games. I wanted to be part of it," she smiles.

Image caption
Volunteers are rewarded with pins and stickers

The volunteers have many different jobs such as venue assistance, transport and medical support.

Massaging the world's greatest athletes doesn't sound like a bad gig. Across at the Olympic Stadium, Mike Whittaker has spent the day manipulating the tired muscles of up to 20 competitors "from the little fast guys to the big hammer throwers". The famous and the unknown have laid on his table.

He is a local PE teacher and a coach at Newham and Essex Beagles, the home club of 2012 Olympians like Mo Farah, Christine Ohuruogu and Chris Tomlinson. Working at the venue, he says simply, is "heaven".

"It's going to be a terrible loss and a massive gap in everybody's lives when it ends," he says. "It'll be very strange not getting up at 4.30 in the morning and getting home at midnight from this."

It's clear as you explore the park that not every volunteer has lucked out in the best role. Games Maker stewards are standing with their backs to the action, watching the crowd instead. Many are found out the back or down in the bowels of venues, endlessly opening the same door for people passing through.

The job they have may not make best use of their skills and brainpower - a maths graduate is checking tickets and helping with enquiries at the Basketball Arena. A teacher from nearby Woodford Green has what he calls a "pen and clipboard" job ticking swimmers on and off the bus at the practice pools at Eton Manor.

In material terms they have just pin badges and stickers on their passes to show for their efforts. Some will give yet more time to staff the Paralympics.

But volunteers are one of the factors that have so far made the Games a success. It is a formula partly forged in 2000 when Sydneysiders took on the idea of welcoming the world to their city.

Park visitors say they make the difference. "They are just everywhere to help, so it's great," says Mel Lewis. "They make the atmosphere fantastic," says Laura Wise, as they walk to the stadium for a night of athletics.

And they are making their families beam. "I am so proud of her, that she does something so unbelievably emotional as her job and then comes here as a volunteer, it's a lot to do," says Wendy Morgan, of her intensive care nurse turned volunteer daughter Laura.